This application is based on Patent Application No. 11-134687 (1999) filed May 14, 1999 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a printing apparatus and a printing method performing control for restricting consumption of power and rise of temperature associated with driving of a printing head.
2. Description of the Related Art
One of important performances of printing apparatus, such as printer or the like, is a printing speed.
Therefore, in a serial scanning type printing apparatus printing an image by scanning a printing head in a direction perpendicular to a transporting direction of a printing medium, for example, a method of increasing number of printing elements to be formed in the printing head has been taken for expanding a region to be printed in one scan and for improving a printing speed.
However, in this case, when the printer is designed under a premise that all of printing elements of the printing head are driven over entire scanning range in one path of scan, various problems, such as increasing of cost and so on, can be encountered.
One of the problems is that capacity of power supply, cost and size of the apparatus are increased, as all of the printing elements are driven at a time. Also, in the case of a thermal type or an ink-jet-type printing head employing an electrothermal transducer as the printing element, another problem of elevating of temperature of the printing head may be caused by simultaneously driving all printing elements. In order to restrict elevating of the temperature in the printing head, it becomes necessary to provide a relatively large head sink (heat radiation plate), for example.
On the other hand, most of the characters or graphic patterns, such as graphic charts and the like to be printed in normal printing or half tone images of photographs and the like may contain pixels to be printed less than or equal to 50% of total number of pixels which can be printed at one path of printing scan.
In view of this, a method to restrict power consumption in one path of scan and not requiring to preliminarily increase a power source capacity in consideration of driving of all printing elements, has been known conventionally.
As one method, a method to aggregate number of printing pixels (number of dots) corresponding number of times of driving of respective printing elements in one printing scan, to lower motion speed of the printing head in the printing scan, accordingly to restrict the power consumption by lowering of a driving frequency of the printing element when dot number exceeds a predetermined number, has been known.
As other method, there has been known a printing method, in which number of dots is aggregated in similar manner as that set forth above, a region to be completed by one path of printing scan depending upon the number of dots is printed over several times of divided scan to restrict power consumption.
On the other hand, in the case of the thermal type printer employing the electrothermal transducer, a printing method restricting elevating of the temperature of the printing head by restricting power consumption depending upon the temperature of the printing head has been known, in order to prevent the printing head from breakage due to elevation of temperature thereof.
However, in the case of the conventional printing method set forth above, the construction becomes complicate for branching of control for printing.
In case of the printing method to lower motion speed of the printing head as set forth above, two or more controls are required in connection with drive control of the motor as a driving source, and optimization becomes necessary in acceleration and deceleration control in respective drive control. On the other hand, in this case, optimization of structure is required even for the motor so as to adapt to various driving speed.
On the other hand, in the case of the printing method to dividingly perform printing for the area to be printing in one path of printing scan, in comparison with control to alternately perform scanning operation of the normal printing head (primary scan) and transporting of the printing medium (auxiliary scan), it becomes necessary to perform exceptional control so as not to perform auxiliary scan during the primary scan. In this case, control becomes complicate.
The present invention has been worked out in view of the problems set forth above. Therefore, it is an object of the preset invention to provide a printing apparatus and a printing method which is simply in control, efficient in printing and can lower power consumption of a printing head.
According to an aspect of the present invention, a printing apparatus employing a printing head having a plurality of printing elements and performing printing by scanning the printing head relative to a printing medium, comprising: counting means, for summing the number of printing dots of printing data corresponding to the number of driving the printing elements prior to scanning of the printing head, the summing being performed by adding, as a unit, the printing data on a band in the scanning direction corresponding to each group of the printing elements in the case the plurality of recording elements are divided into a plurality of groups; judgment means for making judgment whether the number of printing dots summed by the counting means is in excess of a predetermined value; and print control means for selecting a band capable of printing by the scanning depending upon judgment of the judgment means and performing printing by the printing elements corresponding to the selected band.
The print control means may select band associated with summing up to the predetermined value when judgment is made that the number of printed dots exceeds the predetermined value by the judgment means and perform the printing scan using the printing elements corresponding to the selected band.
The print control means may further comprise transport control means for feeding a printing medium for a region corresponding to the band selected in the printing scan.
On the other hand, temperature detecting means for detecting a temperature of the printing head may be further provided and the predetermined value may be varied depending upon the temperature of the printing head detected by the temperature detecting means.
According to another aspect of the present invention. a printing method employing a printing head having a plurality of printing elements and performing printing by scanning the printing head relative to a printing medium, comprising: counting step, for summing the number of printing dots of printing data corresponding to the number of driving the printing elements prior to scanning of the printing head, the summing being performed by adding, as a unit, the printing data on a band in the scanning direction corresponding to each group of the printing elements in the case the plurality of recording elements are divided into a plurality of groups; judgment step of making judgment whether the number of printing dots summed by the counting is in excess of a predetermined value; and
printing step of selecting a band capable of printing by the scanning depending upon the judgment and performing printing by the printing elements corresponding to the selected band.
According to the present invention, when judgment is made that the number of printing dots summed per band in advance of printing scan is in excess of the predetermined value, the printing elements of the bands associated with summing up to the predetermined dot number are driven to perform printing scan. Therefore, the power required for driving the printing head in one printing scan can be restricted to a value corresponding to the predetermined value. As a result, possible largest number of scanning lines can be printed within the range of electric energy consumption allowed for one scan. Thus, efficient printing operation can be performed.
Furthermore, by providing the temperature detecting means for detecting the temperature of the printing head, and by varying the predetermined value depending upon the detected temperature of the printing head, heating value associating with printing operation of the printing head can be restricted.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.